Abstract

This thesis describes the technical development of a novel semiconductor device design aimed at realizing short wavelength visible light emitters. The device structure, called the graded injector, achieves minority carrier injection in a heterojunction system with unfavorable type-II band alignment. Band edge engineering with an alloy graded intermediary layer effectively reduces the conduction band offset and allows for efficient minority carrier injection. The basic device structure consists of a n-CdSe/Mg[subscript x]Cd[subscript 1-x]Se/p-ZnTe heterojunction, where the Mg[subscript x]Cd[subscript 1-x]Se region is graded.

The device design, materials growth, and characterization of II-VI green LEDs based on this structure are presented. Simulations demonstrate the operating principle of the graded injector. Early device development had been hindered by the lack of a p-type dopant for MBE ZnTe and the unavailability of high quality substrates. These restrictions have been overcome with the development of efficient nitrogen p-type doping of ZnTe and the growth capability of high quality heteroepitaxy on GaSb substrates. The materials characterization of the Mg-chalcogenides has enabled more accurate band edge engineering necessary for an operating device.

The advances in growth technology and materials characterization have been incorporated to grow and fabricate working graded injector LEDs. The operating characteristics of these devices unequivocally demonstrate the diode-like operation and efficient minority carrier injection. The electrical and optical performance of these devices will be presented and analyzed.